Where a blade airfoil is part of a two-stage turbine driving a compressor (i.e. part of a high pressure or HP turbine), the requirements for such a blade airfoil design are significantly more stringent than multiple stage airfoil designs, as the compressor relies solely on this two-stage HP turbine to deliver all the required work, as opposed to work being spread over several turbine stages. Over and above this, the airfoil is subject to flow regimes which lend themselves easily to flow separation, which tend to limit the amount of work transferred to the compressor, and hence the total thrust or power capability of the engine. The HP turbine is also subject to harsh temperatures and pressures, which require a solid balance between aerodynamic and structural optimization.